html自动切换背景图片

背景图片每隔一段时间自动切换js代码：

<script type="text/javascript">
       window.onload=function(){
            var imgs =["img/bj1.png","img/bj2.png","img/bj3.png","img/bj4.png","img/bj5.png","img/bj6.png","img/bj7.png","img/bj8.png","img/bj9.png","img/bj10.png","img/bj11.png","img/bj12.png"];//（设定想要显示的图片）
            var i =0;
            var head=document.getElementById("head");//获取DIV对象
            head.style.background="url(img/bj11.png)"; //设置图片的初始图片为该路径的图片
                    function time(){
                            i++;
                            i=i%12;// 超过12则取余数，保证循环在0-12之间
                            head.style.background="url("+imgs[i]+")";}                                               
            setInterval(time,5000);//循环调用time1()函数，时间间隔为5000ms
                    //setInterval()函数，按照指定的周期（按毫秒计）来调用函数或表达式
            }
</script>